Re: [Qemu-devel] [PATCH] configure: check for EFD_NONBLOCK | EFD_CLOEXEC flags

[Stefan Hajnoczi]

On Mon, Nov 21, 2011 at 12:54 AM, Max Filippov <address@hidden> wrote:
> Add check for the EFD_NONBLOCK and EFD_CLOEXEC flags to the
> CONFIG_EVENTFD test.
> This fixes the following build failure on Fedora 9:
>
>      CC    event_notifier.o
>    event_notifier.c: In function `event_notifier_init':
>    event_notifier.c:21: error: `EFD_NONBLOCK' undeclared (first use in this 
> function)
>    event_notifier.c:21: error: (Each undeclared identifier is reported only 
> once
>    event_notifier.c:21: error: for each function it appears in.)
>    event_notifier.c:21: error: `EFD_CLOEXEC' undeclared (first use in this 
> function)
>    make: *** [event_notifier.o] Error 1
>
> Signed-off-by: Max Filippov <address@hidden>
> ---
>  configure |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

At first this patch seemed suspicious because is undefines
CONFIG_EVENTFD on hosts that previously had it defined.  A graceful
fallback that sets nonblocking and close-on-exec using fcntl(2) is
possible, so we don't *need* to be as aggressive as this patch.

However, I chased up the dependencies and it doesn't seem worth doing.
 CONFIG_EVENTFD is a dependency for vhost-net, aio=native, and has
fallbacks elsewhere in QEMU.  Given that vhost-net was merged in
2.6.34 and the eventfd open flags were introduced in 2.6.27, I think
the only feature we actually risk losing here is Linux AIO
(aio=native).

2.6.27-based kernels are old so I'm happy with this change.

Stefan